The challenge for any effort to revise a phenomenologically based diagnostic classification scheme is to make it better, that is, more clinically valuable and more biologically valid. The state of the psychiatric diagnostic manual is, in reality, not much different from that of a variety of other disorders, ranging from irritable bowel syndrome, the epilepsies and dystonias, fibromyalgia, and chronic fatigue syndrome. In retrospect, none of this is surprising, as the complexity of brain development and of the central nervous system, with its 100 billion neurons that make 500 to 800 billion connections, involves thousands of unique cell types, and influences behavior as an emergent phenomenon of interacting genetic programs and complex environmental experience. Similar disappointments occurred in an earlier wave of unbridled enthusiasm from brain imaging studies, both structural and functional, which yielded much about the neurobiology of the major psychiatric disorders, but without any pathognomonic findings that could be incorporated into DSM-5. Moreover, our understanding of the underpinnings of the genetic basis of disease vulnerability and treatment response has become considerably more sophisticated because of, to name a few emerging disciplines, epigenetics, non-coding RNAs, microRNAs, transcriptomics, and proteomics. However, that promise has not been realized in psychiatry, nor in many other branches of medicine, although historic insights about the genetic architecture of complex diseases have emerged. This unbridled enthusiasm followed on the heels of the sequencing of the human genome and the then-existing strong belief that many complex diseases in medicine would be simplified by the results of genome-wide association studies. Because the risk for these disorders has a major genetic component, it seemed plausible to anticipate including specific genetic markers such as single nucleotide polymorphisms or structural genomic abnormalities, (for example, copy number variations), that increase disease vulnerability and perhaps denote biologically distinct alternative phenotypes. When the DSM-5 process was launched several years ago, the clear hope by all involved was that, finally, psychiatric diagnoses would include, in addition to signs and symptoms, various biomarkers of the major disorders including schizophrenia, bipolar disorder, and major depression, with reasonable measures of sensitivity and specificity. Certainly, no such rancor accompanied the release of the 10th edition of the International Classification of Disease (ICD-10). Any such large undertaking, whether it is the introduction of a new healthcare plan for a nation, or the revision of a diagnostic classification of disease, often does provoke spirited debate, but the criticism of DSM-5 from both within and outside the psychiatric community has been exceptional. It is unlikely that when the planning for the fifth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) began 10 years ago, there was any inkling that the process and the final product would engender such a remarkable level of criticism, rhetoric, and passion as we have now witnessed. His research interests include the basic neurobiological and genetic mechanisms of neuropsychiatric disorders, especially schizophrenia. Daniel Weinberger is Director and CEO of the Lieber Institute for Brain Development John Hopkins University School of Medicine, and Professor of Psychiatry, Neurology, and Neuroscience at the McKusick-Nathans Institute of Genetic Medicine.
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